Fluxing action of illite and microcline in a triaxial porcelain body

Abstract

Comparative studies were made on two types of triaxial porcelain bodies; one used conventional potash feldspar ( ST0) and the other used illite ( IT0) as the fluxing agents. Scanning electron micrographs showed that densification and mullite formation in the IT0 body had already occurred at 1000 °C suggesting that there was enough liquid to assist densification and mullite crystal growth. In the ST0 body, mullite crystals started to emerge around 1100 °C, while potash feldspar completely melted around 1200 °C. Full vitrification of the ST0 body required the firing temperature of 1300 °C, which was around 50 °C higher than the IT0 body. The IT0 body showed superior strength to the ST0 body at all studied firing temperature ranges and thus was possibly due to (i) a better densification, (ii) a higher amount of interlocking mullite crystals and (iii) the smaller amounts of residual quartz.